Heat pump apparatus and operation method for heat pump apparatus

ABSTRACT

This description relates to a heat pump and a method of using the heat pump. The heat pump includes a hydraulic compressor that compresses a heat medium, an oil separation and recovery device that separates oil from the heat medium discharged from the compressor and returns the separated oil to the compressor, a condenser that liquefies the heat medium compressed in the compressor, a decompression device that decompresses the heat medium liquefied in the condenser, and an evaporator that causes the heat medium to absorb heat. The aforementioned devices are connected in series and the heat medium is circulated in those devices. The heat medium can be compressed at a compression ratio, at which a discharge temperature from the compressor becomes 150 to 200° C. An intake temperature control unit which can control the temperature of the heat medium taken into the compressor is on the intake side of the compressor.

TECHNICAL FIELD

The present invention relates to a heat pump apparatus and an operationmethod for the heat pump apparatus, and more particularly to a heat pumpapparatus and an operation method for this heat pump apparatus that canincrease thermal efficiency even at a high discharge temperature of acompressor, which is at equal to or higher than 150° C., and that can beoperated stably.

BACKGROUND ART

A oil-flooded screw compressor and a heat pump using the oil-floodedscrew compressor are known. The oil-flooded screw compressor is providedwith an oil circulation system in which oil is supplied to lubricationlocations such as a bearing lubrication unit and a rotor chamber in thescrew compressor, the supplied oil is discharged together withcompressed gas from the discharge port of the screw compressor, thedischarged mixture of compressed gas and oil is subjected to gas-oilseparation in an oil separator, the recovered oil is cooled in an oilcooler, and the cooled oil is again supplied to the lubricationlocations, thereby ensuring circulation and reuse of the oil.

There is a demand for improved performance of the oil-flooded screwcompressor and the heat pump using the oil-flooded screw compressor. Oneof techniques relating to the oil-flooded screw compressor and the heatpumps using the oil-flooded screw compressor that have improvedperformance is disclosed in Patent Document 1. This technique uses nooil cooler in the oil system supplying the oil from the oil separator tothe lubrication locations. Where it is necessary to cool the oil, partof the oil is mixed with a refrigerant system, cooled by therefrigerant, and supplied to the screw compressor therewith. Since nooil cooler is provided, the technique disclosed in Patent Document 1 isfree from waste of heat in the oil cooler. The resultant advantage isthat thermal efficiency of the entire heat pump is high.

-   Patent Document 1: Japanese Patent Application Publication No.    H9-243184

DISCLOSURE OF THE INVENTION

In the field of high-temperature heat pumps, a demand has recently beencreated for a heat pump with a waste heat utilization above 120° C. inwhich the temperature of heat medium discharged from a screw compressoris above 120° C. Further, in the so-called VRC (vapor recompression) inwhich gas discharged from a distillation tower top is recompressed by ascrew compressor and the compression heat created by the recompressionis used, instead of the conventional steam, for boil-up in a reboiler, aheat pump for more than 150° C. is required in which the temperature ofheat medium discharged from a screw compressor is equal to or higherthan 150° C.

However, the technique disclosed in Patent Document 1 is not assumed touse a heat pump with a screw compressor discharge temperature above theaforementioned temperature of 120° C. and further above 150° C.Therefore, in applications to systems with a screw compressor dischargetemperature above the aforementioned temperature of 120° C. and furtherabove 150° C., some problems remain unsolved, those problems beingassociated with modification of heat medium, heat resistance of thescrew compressor, and oil circulation inside the screw compressor.

The present invention has been created to resolve the problems inherentto the conventional technique and it is an object thereof to provide aheat pump in which thermal efficiency is increased by using aconfiguration including no oil cooler and which can be used even at ahigh temperature of heat medium discharged from a screw compressor thatis equal to or higher than 150° C.

In order to solve the above-described problems, the present inventionprovides a heat pump apparatus in which a hydraulic compressor thatcompresses a heat medium, an oil separation and recovery device thatseparates oil from the heat medium discharged from the compressor andreturns the separated oil to the compressor, a condenser that liquefiesthe heat medium compressed in the compressor for heat dissipation, adecompression device that decompresses the heat medium liquefied in thecondenser, and an evaporator that causes the heat medium decompressed inthe decompression device to absorb heat and be evaporated are connectedin series in a heat medium circulation path and the heat medium iscirculated in those devices, this heat pump apparatus beingcharacterized in that a heat medium that can be compressed at acompression ratio, at which a discharge temperature from the compressorbecomes 150 to 200° C., is used as the heat medium, and an intaketemperature control unit which can control the temperature of the heatmedium taken into the compressor is provided in the heat mediumcirculation path on the intake side of the compressor.

Where the discharge temperature of the heat medium from the compressoris made 150 to 200° C., thermal balance including also the oil suppliedto the hydraulic compressor is assumed. As a result, it is unnecessaryto provide an oil cooler that cools the oil separated by the oilseparation and recovery device and returned to the compressor.Therefore, the entire apparatus relating to the compressor is reduced insize and the COP (Coefficient of Performance) is increased because theheat is not dissipated by the oil cooler.

Parts located inside the compressor and exposed to a high temperatureequal to or higher than 150° C. should be produced using materialshaving heat resistance sufficient to withstand a high temperature equalto or higher than 150° C. Further, since the oil is also exposed at alltimes to a high temperature equal to or higher than 150° C. during theoperation of the compressor, an oil should be used that is notdecomposed at a high temperature equal to or higher than 150° C.

By providing the intake temperature control unit, it is possible tocontrol as appropriate the temperature of the mixture of heat medium andoil that is located inside the compressor and discharged from thecompressor. As a result, the interior of the compressor is preventedfrom being unnecessarily heated to a high temperature, the constituentparts of the compressor and oil can be prevented from being deterioratedby a high temperature, and safe operation can be performed.

The heat medium may be a hydrocarbon refrigerant, preferably a C4-C7hydrocarbon. For example, n-hexane, n-pentane, or isopentane may beused.

Further, the heat pump apparatus may be provided with a temperaturesensor which detects the discharge temperature of the compressor, and atemperature control unit which sets a target temperature of thetemperature sensor, issues a command to the intake temperature controlunit, and controls an intake temperature of the heat medium taken to thecompressor so that a detected value of the temperature sensor is thetarget temperature.

As a result, by controlling the intake temperature so that the dischargetemperature of the compressor becomes the target temperature, it ispossible to prevent more reliably the discharge temperature of thecompressor from being unnecessarily high and the constituent parts ofthe compressor and oil from being deteriorated by such high temperature.

The discharge temperature of the compressor is a temperature of themixture of the heat medium and oil discharged from the compressor, butthis temperature is equal to the temperature of an oil retention sectionin the lower portion of the oil separation and recovery device.Therefore, it can be assumed that the temperature sensor detects thetemperature of the oil retention section of the oil separation andrecovery device.

The method in accordance with the present invention that resolves theaforementioned problems is an operation method for a heat pump apparatusin which a hydraulic compressor that compresses a heat medium, an oilseparation and recovery device that separates oil from the heat mediumdischarged from the compressor and returns the separated oil to thecompressor, a condenser that liquefies the heat medium compressed in thecompressor for heat dissipation, a decompression device thatdecompresses the heat medium liquefied in the condenser, and anevaporator that causes the heat medium decompressed in the decompressiondevice to absorb heat and be evaporated are connected in series in aheat medium circulation path and the heat medium is circulated in thosedevices, this method being characterized in that a heat medium that canbe compressed at a compression ratio, at which a discharge temperaturefrom the compressor becomes 150 to 200° C., is used as the heat medium,and a heat-keeping operation is performed by controlling the intaketemperature of the heat medium taken into the compressor so that thedischarge temperature of the compressor reaches a target temperature.

The heat-keeping operation is performed after a warm-up operation hasbeen performed in which the heat medium is heated to a temperature equalto or higher than a boiling point at an intake pressure of thecompressor.

For example, a hydrocarbon such as n-hexane, n-pentane, or isopentanecan be used as the heat medium. Those media have a low boiling point ata normal temperature and are highly probable to be in a liquid statewhen the apparatus operation is started. Accordingly, by performing thewarm-up operation, it is possible to prevent the liquid heat medium frombeing introduced into the compressor.

As described hereinabove, in accordance with the present invention, itis possible to provide a heat pump in which thermal efficiency isincreased by using a configuration including no oil cooler and which canbe used even at a high temperature of heat medium discharged from ascrew compressor that is equal to or higher than 150° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the heat pump according toEmbodiment 1 and a peripheral equipment thereof.

FIG. 2 is a configuration diagram relating to temperature control of thegas taken into the screw compressor.

FIG. 3 is a cross sectional view of the screw compressor in Embodiment1.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained below by using an embodimentillustrated by the appended drawings. The dimensions, materials, shapes,and mutual arrangement of constituent parts described in the embodimentare not intended to restrict the scope of the present invention, unlessspecifically indicated otherwise, and merely represent a simpleillustrating example.

Embodiment 1

FIG. 1 is a schematic diagram illustrating the heat pump according tothe embodiment and a peripheral equipment thereof. The configuration ofthe apparatus will be explained below with reference to FIG. 1. In FIG.1, the reference numeral 1 stands for a heat pump. The heat pump 1 isconfigured by arranging a screw compressor 4, a condenser 6, a tank 8,and an evaporator 10 in a circulation circuit 2. In the heat pump 1, theheat medium circulates in the circulation circuit 2 in the followingorder: screw compressor 4, condenser 6, tank 8, evaporator 10, and screwcompressor 4. A heat medium that can be compressed at a compressionratio such that the intake temperature to the screw compressor 4 is 60to 100° C. and the discharge temperature from the screw compressor 4 is150 to 160° C. is used as the aforementioned heat medium. Morespecifically, C4-C7 hydrocarbons, in particular, n-hexane, n-pentane,and isopentane can be used. Further, in FIG. 1, the reference numeral 12stands for a distillation tower. In the present embodiment, thedistillation tower 12 distills a distillation object which is anazeotropic mixture.

The operation of the apparatus is explained below with reference to FIG.1.

First, the operation of the heat pump 1 is explained.

The heat medium from which heat has been taken by the below-describedazeotropic vapor mixture becomes a gas with a temperature of 60 to 100°C. that is sucked in by the screw compressor 4. The heat medium suckedinto the screw compressor 4 is compressed to a discharge temperature of150 to 160° C. and transferred to the condenser 6.

The below-described distillation object in a liquid state is suppliedfrom the distillation tower 12 into the condenser 6.

In the condenser 6, heat exchange takes place between the heat mediumand the distillation object in a liquid state. The heat medium is cooledand liquefied by the heat exchange and supplied to the tank 8.

The liquid heat medium supplied to the tank 8 is depressurized in thetank 8 and supplied to the evaporator 10.

In the evaporator 10 the heat medium exchanges heat with thebelow-described azeotropic vapor mixture from the top of thedistillation tower 12. The heat medium is heated and gasified by theheat exchange and returned as a gas with a temperature of 60 to 100° C.to the screw compressor 4.

Meanwhile, in the distillation tower 12, part of the distillation objectin a liquid state that is located inside the distillation tower 12circulates in the heating circuit 14. The part of the distillationobject in a liquid state circulating in the heating circuit 14 is heatedby exchanging heat with the heat medium in the condenser 6 disposed inthe heating circuit 14, and heat necessary for the distillationperformed in the distillation tower 12 is supplied. Thus, the condenser6 acts as a reboiler.

Since heat is supplied in the condenser 6 acting as a reboiler by theheat medium to the liquid distillation object circulating in the heatingcircuit 14, part of the distillation object, which is an azeotropicmixture, becomes an azeotropic vapor mixture. The azeotropic vapormixture is supplied from the top of the distillation column 12 to theevaporator 10. The azeotropic vapor mixture supplied to the evaporator10 exchanges heat in the evaporator 10 with the liquid heat mediumsupplied from the tank 8. Because of the heat exchange, the heat mediumis heated and gasified, as described hereinabove, and the azeotropicvapor mixture is cooled, liquefied and supplied to a separation layer16. The azeotropic mixture supplied to the separation layer 16 isseparated into two phases (liquid-liquid) in the separation layer 16.The phase having an entrainer as the main component, from among theliquid phases separated in the separation layer 16, is supplied to adistillation tower (not shown in the figure) separate from thedistillation tower 12 to remove accumulated impurities, theconcentration of the accumulated impurities is decreased as necessary,and the mixture is returned to the distillation tower 12. Part of thephase including as the main components the impurities for which theconcentration is not wished to be reduced by azeotropic distillation,from among the liquid phases separated in the separation layer 16, isreturned through a line 18 into the distillation tower 12 to attain thedesired reflux ratio.

In the above-described configuration and operation, a heat medium thatcan be compressed at a compression ratio such that the intaketemperature to the screw compressor 4 is 60 to 100° C. and the dischargetemperature from the screw compressor 4 is 150 to 160° C., morespecifically, C4-C7 hydrocarbons, in particular, n-hexane, n-pentane,and isopentane is used, as mentioned hereinabove, as the aforementionedheat medium. C4-C7 hydrocarbons such as n-hexane, n-pentane, andisopentane all have a low boiling point and easily can be in a liquidstate at a normal temperature. Therefore, they should be heated beforethe apparatus shown in FIG. 1 is started.

Further, the intake gas temperature to the screw compressor 2 should becontrolled to prevent the temperature of the gas sucked into the screwcompressor 2 from decreasing and the gas from liquefying during theoperation.

In addition, it is necessary to ensure safe operation such that theusage limit of the constituent parts of the screw compressor and thelubricating oil is not exceeded at a high temperature of 150 to 160° C.Therefore, the abrupt increase in the discharge gas temperature of thescrew compressor 4 should be prevented. For this purpose, the intake gastemperature of the screw compressor 4 should be controlled.

FIG. 2 is a configuration diagram relating to intake gas temperaturecontrol of the screw compressor. The devices and equipment relating toFIG. 2, with the exception of the screw compressor 4, are not shown inFIG. 1.

Initially, the supply of oil to the screw compressor will be explainedwith reference to FIG. 2.

In a screw compressor, gas compression is performed in three steps,namely, intake, compression, and discharge, by meshing together theteeth of a male rotor and a female rotor. By spraying oil on the meshingportions of the rotors, it is possible to drive the female rotor withthe male rotor. In addition, gas sealing ability in the gap between therotors and other gaps is increased, the efficiency can be increased bycompressed gas cooling, large-volume gas processing can be performed ata high-speed revolution due to a high volume efficiency and adiabaticefficiency, the friction portions are reduced, a one-stage pressureratio is increased, and the effect produced by liquid return is reduced.This is why the oil is supplied to the screw compressor.

The oil stored in the oil separator 42 is pumped by an oil pump 46 intothe screw compressor 4 and supplied to the lubrication locations such asrotor meshing portions inside the screw compressor 4. The oil suppliedto the screw compressor 4 is mixed with the heat medium gas inside thescrew compressor 4 and mixed with the gas discharged from the screwcompressor 4. The mixture of oil and compressed gas discharged from thescrew compressor 4 is supplied to the oil separator 42. The mixture ofoil and compressed gas is subjected to gas-liquid separation in the oilseparator 42, the oil is again pumped into the screw compressor 4 by thepump 44, and the heat medium gas is supplied to the condenser 6 shown inFIG. 1.

The oil used herein is exposed at all times to a high temperature equalto or higher than 150° C. during the operation of the screw compressor4. Therefore, an oil that is not decomposed or deteriorated at a hightemperature equal to or higher than 150° C. should be used.

The temperature control of the gas taken into the screw compressor willbe explained below with reference to FIG. 2.

The temperature of the liquid phase portion of the oil separator 42,that is, the temperature of oil, is detected by a temperature sensor 44that can detect the temperature of the liquid phase portion of the oilseparator 42. The temperature detected by the temperature sensor 44 istaken into a temperature regulator 22. The temperature detected by thetemperature sensor 44 can be considered to be equal to the temperatureof gas discharged from the compressor 4.

The temperature of the liquid phase portion of the oil separator 44,that is, the target value (for example, 160° C.) of the temperature ofgas discharged from the compressor 4, is set in advance in thetemperature regulator 22. The temperature regulator 22 compares thetemperature detected by the temperature sensor 44 with the target value,calculates the adequate intake temperature, and regulates a heatexchanger 24 provided at the intake side of the compressor 4 in the heatmedium circulation circuit 2 and a bypass valve 26 provided in thebypass circuit of the heat exchanger 24. The configuration of the heatexchanger 24 is not particularly limited, provided that the temperatureof heat medium can be regulated. For example, an air-cooled heatexchanger with fan control and a water-cooled heat exchanger withcooling water amount control can be used.

In the configuration relating to the temperature control of the gastaken into the screw compressor shown in FIG. 2, when the temperaturedetected by the temperature sensor 44 is higher than the target value(for example, 160° C.) that has been set in the temperature regulator,the intake gas temperature is adjusted to a lower temperature byregulating the operation of the heat exchanger 24 and adjusting theopening degree of the bypass valve 26. Meanwhile, when the temperaturedetected by the temperature sensor 44 is lower than the target value(for example, 160° C.) that has been set in the temperature regulator22, the intake gas temperature is adjusted to a higher temperature byregulating the operation of the heat exchanger 24 and adjusting theopening degree of the bypass valve 26. As a result, stable operation canbe performed, without exceeding the usability limit of the constituentparts of the screw compressor and the lubricating oil at a hightemperature.

As mentioned hereinabove, a C4-C7 hydrocarbon, for example, n-hexane,n-pentane, and isopentane, is used as the heat medium. However, sinceall those compounds have a low boiling point and can be easilyliquefied, it is possible that the intake gas temperature will abruptlydecrease and the gas will be condensed. Accordingly, it is desirablethat a knock-out drum (KO drum) 28 be disposed downstream of the heatexchanger 24 and upstream of the screw compressor 4 so that thecondensed gas will be prevented from entering the screw compressor 4even in this case.

Further, the configuration shown in FIG. 2 can be also used during awarm-up operation performed when the apparatus is started. In this case,the oil alone is initially circulated in the order of compressor 4→oilseparator 42→oil pump 46. Then, the heat medium heated, for example, bya heater (not shown in the figure) provided in the tank 8 is sucked intothe screw compressor 4, while the temperature measured by thetemperature sensor 44 is being monitored and the heat exchanger 24 andthe bypass valve are being adjusted by the temperature regulator 22.

FIG. 3 is a cross-sectional view illustrating the screw compressor 4according to the embodiment. In FIG. 3, the reference numeral 101 standsfor a casing. The male rotor 2 and the female rotor 3, which are in theform of helical gears with different numbers of teeth, are accommodatedinside the casing 1 so that the rotors mesh together and rotate inopposite directions.

The reference numerals 107 and 109 stand for bearings on the male rotorside. The shaft of the male rotor 102 is rotatably supported by thebearings 107 and 109 at the casing 101. The reference numerals 108 and110 stand for bearings on the female rotor side. The shaft of the femalerotor 103 is rotatably supported by the bearings 108 and 110 at thecasing 101.

The reference numeral 111 stands for a thrust bearing on the male rotorside. The thrust load of the male rotor 102 is taken up by the casing101 via the shaft of the male rotor 102 and the thrust bearing 111.Further, the reference numeral 112 stands for a thrust bearing on thefemale rotor side. The thrust load of the female rotor 103 is taken upby the casing 101 via the shaft of the female rotor 103 and the thrustbearing 112.

The reference numeral 113 stands for a mechanical shaft seal that sealsthe shaft of the male rotor 102.

The reference numeral 114 is a balance piston that is fixedly attachedto the end portion of the shaft of the male rotor 102 on the sideopposite that of the drive side where the thrust load becomes large. Thebalance piston is fitted into the cylinder formed inside the casing 101,so that the piston can reciprocatingly slide therein.

The gaseous heat medium that is introduced into the screw compressor 4during the operation of the screw compressor 4 is compressed anddischarged by volume variations in the gap between the male rotor 102and the female rotor 103 that rotate in mutually opposite directions.

The thrust load generated by volume variations in the gap generated whenthe male rotor 102 and the female rotor 103 rotate is taken up by thecasing 101 via the shaft of the male rotor 102 and the thrust bearing111 on the male rotor 102 side and by the casing 101 via the shaft ofthe female rotor 103 and the thrust bearing 112 on the female rotor 103side.

In the screw compressor 4 shown in FIG. 3, the male rotor 102, femalerotor 103, bearings 107, 108, 109, 110, thrust bearings 111, 112,mechanical shaft seal 113, and balance piston 114 are exposed to a hightemperature of about 150 to 160° C., which is the compressor dischargetemperature of the heat medium, due to the compression of heat mediumand introduction of oil. Therefore, the aforementioned constituentcomponents of the screw compressor should be produced using materialshaving heat resistance sufficient to withstand a high temperature ofabout 150 to 160° C.

Further, the clearance between the casing 101 and the male rotor 102 andthe clearance between the casing 101 and the female rotor 103 can beadjusted to prevent the male rotor 102 and the female rotor 103 fromexposure to an unnecessarily high temperature.

For example, where rotor clearance ratio represented by the clearancebetween the rotor and the casing and the outer diameter of the rotor istaken as 0.0020 (=20/10,000), the increase in the temperature of therotors (male rotor 102, female rotor 103) can be inhibited.

INDUSTRIAL APPLICABILITY

In the heat pump and the operation method therefor in accordance withthe present invention, no oil cooler is provided and therefore thermalefficiency can be increased. Furthermore, the heat pump can be used evenat a high temperature of heat medium discharged from a screw compressorthat is equal to or higher than 150° C.

1. A heat pump apparatus in which a hydraulic compressor that compressesgas to be compressed that is at a temperature equal to or higher than anormal temperature, an oil separation and recovery device that separatesoil from the gas discharged from the compressor and returns theseparated oil to the compressor, a condenser that liquefies the gascompressed in the compressor for heat dissipation, a decompressiondevice that decompresses the gas liquefied in the condenser, and anevaporator that causes the liquefied gas decompressed in thedecompression device to absorb heat and be evaporated are connected inseries in a gas circulation path and the gas is circulated in thosedevices, the heat pump apparatus being wherein a hydrocarbon convertedinto a gaseous state by heating is used as the gas to be compressed thatis taken into the compressor and the compressor is set to be capable ofcompressing the gas at a compression ratio at which a dischargetemperature becomes 150 to 200° C., and a heating unit which heats thegas provided at the intake side of the compressor and an intaketemperature control unit which performs heating control of the heatingunit to be able to control the temperature of the hydrocarbon taken intothe compressor are provided, and the heating control of the heating unitis performed by the intake temperature control unit so that thehydrocarbon is controlled by heating to a gaseous state.
 2. (canceled)3. The heat pump apparatus according to claim 1, wherein the gas to becompressed is a C4-C7 hydrocarbon refrigerant, and the hydrocarbon isheated by the intake temperature control unit to a temperature of 60 to110° C. and used as the gas to be taken into the compressor.
 4. The heatpump apparatus according to claim 1, comprising: a temperature sensorwhich detects the discharge temperature of the compressor, wherein acommand is issued to the intake temperature control unit, and the intaketemperature of the hydrocarbon taken into the compressor is controlledso that a target temperature of the temperature sensor is set to 150 to200° C. and a detected value of the temperature sensor is the targettemperature.
 5. An operation method for a heat pump apparatus in which ahydraulic compressor that compresses a gas to be compressed that is at atemperature equal to or higher than a normal temperature, an oilseparation and recovery device that separates oil from the gasdischarged from the compressor and returns the separated oil to thecompressor, a condenser that liquefies the gas compressed in thecompressor for heat dissipation, a decompression device thatdecompresses the gas liquefied in the condenser, and an evaporator thatcauses the liquefied as decompressed in the decompression device toabsorb heat and be evaporated are connected in series in a gascirculation path and the gas is circulated in those devices, wherein ahydrocarbon converted into a gaseous state by heating is used as the gasto be compressed that is taken into the compressor and the compressor isset to be capable of compressing the gas at a compression ratio, atwhich a discharge temperature becomes 150 to 200° C., and thetemperature the temperature of the hydrocarbon taken into the compressoris controlled by heating to maintain the hydrocarbon in a gaseous stateby means of a heating unit which heats the gas provided at the intakeside of the compressor.
 6. The operation method for a heat pumpapparatus according to claim 5, wherein the hydrocarbon is heated by theheating unit to a temperature equal to or higher than a boiling point atan intake pressure of the compressor before the compressor is operated.